Module 3 Motion Flashcards
What is a scalar quantity?
one which has a magnitude but no direction (and a unit)
What is a vector quantity?
one with a magnitude and direction (and a unit)
How can scalar quantities be used in calculations?
normally, eg added, subtracted, multiplied, and divided in the normal manner
Remember scalar quantities can be negative
Examples of vector quantities
Displacement
Velocity
Acceleration
Force
Momentum
Examples of scalar quantities
Length
Mass
Speed
Time
Temperature
Volume
Potential difference
Power
How can velocity be defined?
rate of change of displacement
What is a resultant vector?
the value found when adding vectors in a vector addition
Resultant vector has magnitude and direction
How to add parallel vectors
simply add them together to find the resultant vector
What does “acting in the same line and direction” mean?
are parallel
What is another word for vectors in opposite directions?
antiparallel
How to add antiparallel vectors ie parallel vectors pointing in opposite directions?
one direction is considered positive the other negative and add them (assume right, or up is positive, and down or left is negative unless told otherwise)
What are perpendicular vectors?
vectors acting at right angles to each other
How to subtract vectors in opposite directions?
add them as you get a–b = a+b
How to find resultant vector of perpendicular vectors?
at right angles so use Pythagoras
a^2 + b^2 = c^2
How to find direction of resultant vectors
Use SOCAHTOA (trigonometry)
Re angle of a vector - What does to the horizontal mean?
use the angle on the horizontal
Re angle of a vector - What does to the vertical mean?
use the angle on the vertical
What is resolving vectors?
splitting a resultant vector into two perpendicular components (vectors)
same as finding the components
What is finding the components of a vector?
splitting a resultant vector into two perpendicular components (vectors)
same as resolving
What are the two formulae used in resolving vectors?
Fcosθ to find the horizontal component (x-axis)
Fsinθ to find the vertical (y-axis)
angle is to the horizontal
How to define speed?
rate of change of distance
How to calculate average speed?
total distance travelled/time taken
What does the gradient of a distance-time graph represent?
speed
What is instantaneous speed?
the speed of an object over a very short interval of time
How do you define velocity?
rate of change of displacement
How to calculate average velocity?
change in displacement/time taken
What is the symbol used for displacement?
s
Why will the displacement of an object always be ≤ the distance?
displacement will be shortest route (as it is a straight line), distance will be actual distance
What does the gradient of a displacement time graph represent?
velocity
What does the area under a velocity time graph represent?
displacement of object
How to calculate the displacement of under a velocity time graph with changing acceleration (ie curved graph)?
use the counting squares method
Find the area of one small square (using your scale)
Count the number of squares that are completely under the graph
Add any squares that are over 50% under the graph
Multiply the area of one square by number of squares
How do you define acceleration?
rate of change of velocity
What does deceleration represent?
negative acceleration (in the opposite direction of velocity)
When looking at velocity-time graphs, what does a straight line with a positive gradient mean in terms of acceleration?
constant positive acceleration
What does a horizontal line in a velocity-time graph represent in terms of acceleration?
constant velocity, zero acceleration
What does a curve mean in terms of acceleration in a velocity time graph?
changing gradient therefore changing acceleration
Define stopping distance?
total distance travelled from when a driver first sees the hazard and when the vehicle stops
What is the thinking distance?
the distance travelled from the point between moment of first seeing the reason to stop and braking
What is braking distance?
distance between applying brakes and the vehicle stopping
How to calculate total stopping distance?
thinking distance+braking distance
List 3 factors that effect stopping distance
Speed of the vehicle
Conditions of the brakes, tyres and roads
the weather conditions
alertness of the driver
How to calculate thinking distance?
speed of vehicle x reaction time
What is the relationship between braking distance as the speed of a car?
distance proportional to u^2
from v^2=u^2 + 2as with v=0
Explain the relationship between braking distance and speed (using KE)
When a car is travelling it has the KE=1/2mu^2
When it brakes it has the
KE=braking force F x distance (formula for work done)
If F, m, and 1/2 constant we can see that
d ∝ u^2
What is the effect on braking distance is speed is tripled?
d ∝ u^2 therefore distance increases by
3^2 = 9
What information do you need to resolve a vector?
the magnitude and direction of a resultant vector
